Optical coherence analysis relies on the use of the interference phenomena between a reference wave and an experimental wave or between two parts of an experimental wave to measure distances and thicknesses, and calculate indices of refraction of an object of interest. Optical Coherence Tomography (OCT) is one example technology that is used to perform usually high-resolution cross sectional imaging that can provide images of objects such as biological tissue structures, for example, on the microscopic scales in real time. Optical waves are sent through an object and a computer produces images of cross sections of the object by using information on how the waves are changed.
The original OCT imaging technique is the time-domain OCT (TD-OCT), which uses a movable reference mirror in a Michelson interferometer arrangement. Another type of optical coherence analysis is termed Fourier domain OCT (FD-OCT). Other terms are time encoded Frequency Domain OCT and swept source OCT. These techniques use either a wavelength swept source and a single detector, sometimes referred to as time-encoded FD-OCT or TEFD-OCT, or a broadband source and spectrally resolving detector system, sometimes referred to spectrum-encoded FD-OCT or SEFD-OCT. FD-OCT has advantages over time domain OCT (TD-OCT) in speed and signal-to-noise ratio (SNR).
TEFD-OCT has advantages over SEFD-OCT in some respects. The spectral components are not encoded by spatial separation, but they are encoded in time. The spectrum is either filtered or generated in successive frequency steps and reconstructed before Fourier-transformation.
Probe design is an important aspect of OCT system design, especially on systems that are intended to analyze the human body, such as medical diagnostic systems. On one hand, the probes must be mechanically robust to withstand use and possibly repeated use by medical care delivery personnel such as doctors, nurses and technicians in clinical settings. The probes should also be robust against noise generated from the use in their intended application. For example, OCT probe systems for intravascular analysis applications are typically long, extending from at least the point of access, such as the femoral artery to the coronary or carotid artery that is to be scanned. Moreover, the probes are often spun at high speed within a sheath while being pulled-back through the artery section of interest to generate a cylindrical scan. Any concomitant mechanical stress on the fiber can induce length changes and birefringence due to twisting. Probes for dental applications typically include a long umbilical that connects the handpiece/optical interface to the OCT analysis system or console; noise introduced in the OCT analysis due to mechanical shock to both the umbilical and handpiece/optical interface should be minimized.